S. Vishnu Sharma
IIT Guwahati and ISRO researchers have made a groundbreaking discovery.
They made this while studying the first known Galactic Ultraluminous X-ray emitting pulsar, Swift J0243.6+6124.
Polarization
The research by IIT Guwahati and ISRO shows that the polarization of X-rays emitted by this pulsar is significantly lower than expected, challenging existing theories of emitted radiations from these astronomical bodies.
Neutron Stars
Neutron stars are formed when a massive star exhausts its fuel and collapses under its own gravity, compressing its core and transforming protons and electrons into neutrons.
If the core’s mass is between one and three times that of the sun, the collapse halts, creating a neutron star, say researchers from IIT Guwahati.
These incredibly dense objects are the most compact known, with a mass like the sun but condensed to the size of a city, say sources from IIT Guwahati.
Many neutron stars are observed as pulsars, emitting regular pulses of radiation as they spin.
X-ray pulsars are a specific type of neutron star in binary systems, where a companion star orbits a highly magnetized neutron star, emitting pulses of X-rays.
Bright
Ultraluminous X-ray sources (ULXs) are bright X-ray emitters from nearby galaxies that were once thought to be intermediate-mass black holes.
However, some are now believed to be pulsars because they emit regular pulses, say sources from IIT Guwahati.
Swift J0243.6+6124, detected by NASA’s Swift spacecraft during a strong X-ray outburst in 2017–2018, was identified as the first Galactic ULX pulsar due to its exceptional X-ray brightness.
Investigating
Researchers worldwide have been investigating the nature of polarized X-ray emissions from Swift J0243.6+6124.
The ISRO and IIT Guwahati scientists focused on this source during its active period in 2023, using NASA’s Imaging X-ray Polarimetry Explorer (IXPE) to detect the polarized X-rays emission for the first time.
They also combined data from the Neutron Star Interior Composition ExploreR (NICER) and the Nuclear Spectroscopic Telescope Array (NuSTAR) missions, say sources from IIT Guwahati.
This approach enabled them to gain a deeper understanding of the energy-dependent characteristics of the X-ray pulses from Swift J0243.6+6124, say sources from IIT Guwahati.
The scientists found that the polarization of X-rays from Swift J0243.6+6124 was much lower than expected, around 3%, say sources from IIT Guwahati.
Impact
Dr Anuj Nandi highlighted the impact of this research.
The IXPE mission’s unique capabilities made it possible to detect low polarization in X-rays from the first known Galactic ULXPs, he said.
‘Notably, this low polarization appears to vary with the emitted pulses.’
Research
Prof. Santabrata Das, Department of Physics, IIT Guwahati spoke about the research.
The discovery of lower polarization in the X-rays from Swift J0243.6+6124 is important because it makes us rethink how these stars work, he said.
Neutron stars in binary systems have very strong magnetic fields that direct matter from a nearby star to their poles, said Prof Santabrata of IIT Guwahati.
This process affects the X-rays we see because the magnetic field influences how the X-rays behave. The polarization of X-rays plays a big role in this, he said.
The unexpected low polarization means our current understanding of these magnetic fields and X-rays needs to be updated, he said.
Challenge
This surprising result challenges current theories and raises new questions for further exploration. It also opens new opportunities for studying similar X-ray sources within our galaxy and beyond.
Publishing
The details of this research have been published in The Astrophysical Journal Letters.
It is co-authored by Dr. Santabrata Das, Dr. Anuj Nandi, and researchers Mr. Seshadri Majumder, Ms. Rwitika Chatterjee, and Mr. Kiran M. Jayasurya.
The paper may be accessed at https://doi.org/10.3847/2041-8213/ad67e5.
About IIT Guwahati
Indian Institute of Technology Guwahati, established in 1994, completed 25 years of glorious existence in 2019.
At present, the Institute has eleven departments, nine interdisciplinary academic centres and five schools.
They cover all the major engineering, science, healthcare, management, and humanities disciplines, offering BTech, BDes, BSc(Hons), MA, MDes, MTech, MSc, MS(R), MBA and PhD programmes.
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The institute offers a residential campus to 439 faculty members and more than 8,600 students at present.